1. Field of the Invention
The present invention relates to an apparatus for measuring flux of a flowable medium, and more particularly, to a flux distribution measuring apparatus for measuring spatial distribution of flow rates of a flowable medium using thin metal wires to scan the flowable medium.
2. Description of the Related Art
There are various types of existing flow rate meters for measuring flow rates of a flowable medium. Typical flow rate meters for measuring flow rates in the vicinity of the atmospheric pressure generally utilize a method for measuring flow rates by rotating a fan, or a method for measuring flow rates by using thermoelectric strips or thermal wires. A thermal wire flow rate meter called an xe2x80x9canemometerxe2x80x9d is an apparatus for measuring flow rates of a flowable medium, particularly turbulence, and there are basically two types of anemometers, a constant temperature anemometer (CTA) and a constant current anemometer (CCA). The CTA employing a negative feedback control theory has more advantages including a fast frequency response characteristic than the CCA, and thus the former is currently more widely used than the latter.
In case of the CTA, externally applied current or voltage is maintained so that a platinum wire of several microns thick reaches a constant temperature, and then a flow rate is determined using the amount of current which is fed back and controlled to keep the constant temperature in response to the changes of an external gaseous flow. That is, since the platinum wire is further cooled as the flow rate becomes larger, more current is demanded. Reversely, as the flow rate becomes smaller, less current is demanded. This is the same as the principle of a Pirani gauge for measuring degree of vacuum under the circumstances of low vacuum.
The above-described conventional flow rate meters can measure flow rates of certain areas of a flowable medium, but have difficulties in measuring spatial distribution of flow rates of a flowable medium. That is, the conventional flow rate meter in which a single elementary sensor is fixed can detect a flow rate at one position, but has the difficulty in measuring those at a number of places simultaneously, due to its spatial limitation. In particular, the conventional flow rate meter has more difficulties in measuring the flow rate under the circumstances of vacuum. As an example, when oxidation films and the like are chemically formed on a silicon wafer in the semiconductor manufacturing process which is performed under the conditions of a total vacuum degree of about several torrs to militorrs, it has been recognized as a crucial factor relating to a yield in the semiconductor manufacturing process to maintain constant the gaseous spray of a shower head for spraying gas at a constant flow rate onto a silicon wafer. However, it is difficult to quantitatively measure distribution of flow rates of the gaseous spray.
To solve the above and other problems, the present invention provides a flux distribution measuring apparatus in which an array of sensors is disposed to scan a flowable medium in the direction perpendicular to its flow path, to thereby detect distribution of flow rates at the scanned surfaces.
In an embodiment according to the present invention, there is provided a flux distribution measuring apparatus comprising: at least one metal thin wire for scanning a flowable medium; current supply lines each connected to each of the ends of the at least one thin metal wire, for providing current flowing through the at least one thin metal wire; and lead wires each connected to the at least one thin metal wire and having a uniform interval between adjacent lead wires, wherein voltage differences each between adjacent ones of the lead wires are detected to measure the distribution of flow rates.